1. Field of the Invention
The present invention relates to a print head for printing images on a reception medium by impinging charged particles on the reception medium.
2. Description of the Related Art
FIG. 1 is a cross-sectional view showing essential configuration of a well known image forming device provided with a recording head.
An image forming device 10 la provided with a toner supply unit 11, which includes a toner case 13 filled with charged particles, such as toner 12. A variety of components are provided within the toner case 13, including a toner supply roller 15, a toner bearing roller 14, and a blade 16. The toner supply roller 15 supplies charged toner to the outer peripheral surface of the toner bearing roller 14. The toner tearing roller 14 has a cylindrical shape and bears, on its outer peripheral surface, the charged toner supplied by the toner supply roller 15. The blade 16 regulates the thickness of the toner layer supported on the outer peripheral surface of the toner bearing roller 14 to a uniform layer thickness.
An aperture electrode member 17 formed with a plurality of apertures is disposed above the toner bearing roller 14. The aperture electrode member 17 is supported with the apertures in confrontation with, and in resilient contact with, the outer peripheral surface of the toner bearing roller 14. The aperture electrode member 17 is formed with a plurality of electrodes in the vicinity of the apertures. The electrodes are for controlling passage of toner 12 from the outer peripheral surface of the toner bearing roller 14 through the apertures.
Detailed configuration of the aperture electrode member 17 will be described while referring to FIGS. 2 to 3 (C). FIG. 2 is a perspective view showing overall configuration of the aperture electrode member 17. FIG. 3 (A) is a magnified view showing a portion of the aperture electrode member 17 shown in FIG. 2. FIG. 3 (B) is a cross-sectional view taking along a line C--C of FIG. 3 (A). FIG. 3 (C) is a magnified view showing an insulation sheet of the aperture electrode member 17 shown in FIG. 3 (A).
As shown in FIG. 2, the aperture electrode member 17 includes an insulation sleet 17a and IC chips 17d disposed on the insulation sheet 17a. The insulation sheet 17a is formed from a synthetic resin, such as polyimide, to a thickness of 25 .mu.m. A plurality of apertures 17b are formed through the insulation sheet 17a, aligned with a lengthwise direction of the insulation sheet 17a. It should be rioted that because the apertures are formed with such a narrow pitch, they are indicated by a straight line in FIG. 2.
An shown in greater detail in FIG. 3 (A), the aperture electrode member 17 also includes control electrodes 17c provided between adjacent apertures 17b, and conductive lines 17e for connecting the IC chips 17d with the control electrodes 17c. With this configuration, the IC chips 17d can apply a control voltage to energize the control electrodes 17c.
As shown in FIG. 3 (B), a coat layer 17f is formed on the lower surface of the insulation sheet 17a, that is, on the surface that directly contacts the outer peripheral surface of the toner bearing roller 14. The coat layer 17f is formed mainly from a polyimide type base binder, but also includes carbon as a conductive material, flourine dioxide for reducing friction force, and a charge control agent (CCA).
Returning to FIG. 1, the image forming device 10 is also provided with a control circuit 18, a DC voltage source 20, a heat roller 22, a pressure roller 23, and a cylindrical back electrode roller 19. The control circuit 18 is for controlling the IC chips 17. Each IC chip 39 of the aperture electrode member 17 is connected to the control circuit 18. The cylindrical back electrode roller 19 is rotatably disposed in confrontation with the aperture electrode member 17 and is connected to a DC voltage source 20. The heat roller 22 and the pressure roller 23 are disposed in confrontation with each other at a position downstream in a transport direction of a reception medium 21 from the back electrode roller 19.
Next, operations of the image forming device 10 will be described. First, the toner supply roller 15 and the toner bearing roller 14 are rotated in a direction indicated by arrows F1 and F2, respectively, of FIG. 1. Rotation of the toner supply roller 15 transports toner 12 stored in the toner case 13 toward the toner bearing roller 14, and scrapes the toner 12 onto the outer surface of the toner bearing roller 14. Resultant friction charges the toner to a negative charge. Next, the blade 16 regulates the toner 12 borne on the outer peripheral surface of the toner bearing roller 14 into a uniform thin layer. Further rotation of the toner bearing roller 14 convoys the thin layer of toner 12 on the toner bearing roller 14 towards the lower surface of the aperture electrode member 31. An a result, this toner 12 borne on the outer peripheral surface of the toner bearing roller 14 is supplied to a position beneath the apertures 17b while being scraped along the lower surface, that is, the coat layer 17f of the aperture electrode member 17.
The control circuit 18 applies, for example, a positive 40 V voltage to selected ones of the control electrode 17c in accordance with inputted image information. Difference in electric potential between the control electrodes 17c and the toner bearing roller 14 generates electric lines of force in the vicinity of the apertures 17b corresponding to control electrodes 17c applied with the voltage by the control circuit 18. The electric lines of force extend from the control electrodes 17c towards the toner bearing roller 14, whereupon the negatively charged toner 12 borne on the outer peripheral surface of the toner bearing roller 14 is drawn towards the high electric potential near the apertures l7b. The toner 12 that separates from the toner bearing roller 14 in this manner is caught in the electric field formed between the reception medium 21 and the control electrodes 17c by a voltage applied to the back electrode roller 19. The toner 12 is that further drawn toward to, and impinged on, the reception medium 21 to form an image by accumulating an the surface of the reception medium 21.
A single line's worth of pixels is formed by controlling passage of toner 12 through the apertures 17b one time. Once a single line's worth pixels has been formed, the back electrode roller 19 is rotated in a direction indicated by an arrow F3 in FIG. 1, in order to transport the reception medium 21 by a single pixel distance. By repeating the above described processes, all lines of an image can be formed in toner on the reception member 21. The toner image is then fixed on the surface of the reception member 21 by the heat roller 22 and the pressure roller 23.